1. Field of the Invention
This invention relates to a user-propelled vehicle or wheelchair. More particularly, it relates to a wheelchair propelled by push levers connected to drive wheels through bicycle chains and variable ratio rear gear clusters.
2. Description of the Prior Art
Most wheelchair users have little or no functional use of their lower extremities, but have preserved normal upper body function. Accordingly, the conventional wheelchair requires the user to propel the chair by repetitively pushing on push-rims attached to the main wheels of the chair. The arm and shoulder motions that are required are undesirable because they utilize the small, relatively weak, muscles of the rotator cuff and ultimately lead to stress injury and degenerative arthritis of the shoulder joint. This is also an inefficient means of locomotion; providing only a one-to-one ratio of distance traveled for distanced pushed. It is, however, an ubiquitous and relatively simple machine that can be easily maintained. Several attempts have been made to improve on this standard with very limited success.
Several inventions employ the use of levers for the user to propel the chair. This is an improvement because it makes use of the larger and more powerful triceps and pectoral muscles, with reduced shoulder stress. Still, however, all of these devices have fallen short of success.
For example, U.S. Pat. No. 4,865,344 provides only one speed having one fixed gear ratio, and thereby forgoes the significant mechanical advantage gained by using a set of multiple gear ratios. This machine also requires the user to steer with hand levers attached to the push levers, increasing the complexity of steering and propulsion movements.
U.S. Pat. No. 5,322,312 is another attempt to propel a wheelchair with a push lever. It also lacks sufficient mechanical advantage, having only one gear ratio. The use of a detachable skateboard device makes this machine unnecessarily complex, expensive, and difficult to maintain.
U.S. Pat. No. 5,209,506 is cumbersome in requiring the user to steer with handlebars which are simultaneously pushed and pulled to propel the chair. The linkage required to operate this machine is also too complex for easy care, and the position of the steering/push lever obstructs easy entry and exit of the chair.
U.S. Pat. No. 4,811,964 also uses push levers for power, but in a rowing motion. This machine would be difficult to steer, having a combined row-steer motion; it also has only one speed, and uses a complex system of pulleys and linkage, all of which serve to make it impractical.
U.S. Pat. No. 3,994,509 is another lever-driven machine that makes use of a very complex and expensive system of forward and reverse clutches. It also provides only a single forward speed, and has a very wide profile, to accommodate the wide-set wheels. There are several inventions that use a set of bicycle pedals to turn a crank which, in turn, transfers power via a bicycle chain to either front or rear wheels. All of these hand-crank designs suffer from the fact that the hand cranking motion is extremely fatiguing. Further, they are too big and too heavy. The cranking/steering device obstructs entry and exit. These wheelchairs generally lack multiple gears and are difficult to steer while cranking.
U.S. Pat. No. 4,720,117 is a typical example of this type of machine.
U.S. Pat. No. 5,362,081 is an attempt to adapt the mechanical advantage of multiple gear ratios to the standard wheelchair format. It does not, however, save the user from the repetitive motion injury and degenerative damage to the shoulder joints; and, in requiring the use of the user smaller, weaker rotator cuff muscles, it is more fatiguing than a push lever driven machine. This particular model also requires the user to let go of the steering/drive wheel to shift gears.
There are designs that use a system of levers and gears to propel the chair, but none of them have all the combined advantages that my invention offers.
Some of those (U.S. Pat. Nos. 6,276,703; 6,557,879; 6,764,089) put the user in a very low position, almost recumbent. This is an impractical position for daily use because of the difficulty in getting down onto the chair and up out of the chair. It also places the user too low to interact with their environment and other people. These frames are only useful in sporting events.
Some of these designs (U.S. Pat. Nos. 5,632,499; 6,173,986; 4,560,181; 6,371,502; 6,715,780) utilize systems that derive power from both pushing and pulling the hand levers. These use various mechanical methods and machinery to provide forward propulsion on both push and pull strokes. The function of pulling on the levers under load to propel the chair is very non-ergonomic; and is only useful for very short periods at very low power.
It is clear to see that a “pushing” motion allows the user to make use of a rigid back rest for passive resistance to the power stroke. This is not possible with the “pulling” motion.
Since wheelchair users have no leg strength, the user must utilize all abdominal muscles and back muscles to stabilize his trunk for each “pulling” motion. This is extremely fatiguing and highly impractical for prolonged mobility.
Some of these designs (U.S. Pat. Nos. 6,820,885; 4,560,181; 6,371,502; 6,557,879; 6,276,703) utilize a variable lever arm length to obtain their version of “gearing”. This is not true gearing, but can provide a differing angular distance of wheel movement with a fixed distance of arm movement. However, the range of this variation is quite limited; and the designers do not take into account the difference in the angular speed of the wheel and how difficult it is to keep up with faster arm motions. Functionally these become single-speed chairs.
Some of these designs (U.S. Pat. Nos. 6,715,780; 6,557,879; 6,276,703) use a wheel hub with internal gears. This is a usable gearing system designed for bicycles over 50 years ago. It has recently been revived in the bicycle world, because the delicate moving parts are all enclosed and protected from the major trauma that mountain bikes regularly encounter. Derailers on mountain bikes have a very short life cycle. These internal gear hubs function in only one orientation, i.e. with the drive chain on the right side as done by U.S. Pat. No. 6,715,780. It is not clear that the other two patents that cite use of an internal drive hub can actually function. Although it is possible to manufacture such a hub that is a complete mirror-image of the standard hub, this is not currently being done nor likely ever will be. The derailer is still superior for a road machine due to its simplicity, lighter weight and greater range of gear ratios.
One design (U.S. Pat. No. 6,674,089) does utilize a derailer for its gearing system. It drives a single rear axle with either one or two wheels, and cannot use these wheels for steering, but must rely on front wheel rotation for steering.
Applicant's previous patent (U.S. Pat. No. 6,234,504) is similar to the current design, with some minor changes, primarily in the reverse function.
Several designs have indicated the use of various braking systems, all of which are obvious and analogous and interchangeable with any other design. The disc brake is not inherently superior nor novel, however it is easy to use with the brake lever set near the user's hand and the braking mechanism is set in a more protected place on the chair making it less likely to be traumatized by the environment.
Some designs indicate differing number and configuration of wheels, shock absorbers, seating material that really have nothing to do with the propulsion mechanism and user needs.